Sectional boiler for flameless combustion of gaseous fuels

ABSTRACT

Sectional boiler comprising reaction chambers filled with ceramic material, an air-gas mixing device arranged in front of the boiler and a fuel mixture supply pipe, attached in the boiler to a fuel distributor, housing a porous refractory diaphragm followed by a combustion space with spark igniting means. Between the diaphragm and the reaction chambers a refractory block is positioned, provided with apertures leading to the reaction chambers. The water space of the boiler is constituted by hollow boiler sections, at least some of their walls being of comb-like formation, to form, when juxtaposed, the reaction chambers.

States Patent Sittek et al.

[75] Inventors: Edvin Sittek, Novy Bohumin;

Jaroslav Katolicky, Detmarovice; .iaroslav Kuba, Skrecen; Edmund Dvorok, Novy Bohumin, all of Czechoslovakia [73] Assignee: Hutni druhovyroba, generalni reditelstvi, Praha, Czechoslovakia [22] Filed: Nov. 8, 1973 [21] Appl. No.: 414,094

[30] Foreign Application Priority Data Nov. l5, 1972 Czechoslovakia 7718-72 [52] U.S. Cl. 122/225 R, 431/326 [51] int. Cl. F22b 7/00 [58] Field of Search 122/223, 225 R, 250; 431/326, 327, 328

[56] References Cited UNITED STATES PATENTS 2,414,557 l/l947 Reed 122/225 Oct. 22, 1974 2,563,2Il 2/197! Hornbostcl. Jl. 122/250 2,563,212 2/1971 Hoagland 2,934,046 4/1960 Donohue 122/225 Primary Examiner-Kenneth W. Sprague [57] ABSTRACT Sectional boiler comprising reaction chambers filled with ceramic material, an air-gas mixing device arranged in front of the boiler and a fuel mixture supply pipe, attached in the boiler to a fuel distributor, housing a porous refractory diaphragm followed by a combustion space with spark igniting means. Between the diaphragm and the reaction chambers a refractory block is positioned, provided with apertures leading to the reaction chambers. The water space of the boiler is constituted by hollow boiler sections, at least some of their walls being of comb-like formation, to form, when juxtaposed, the reaction chambers.

4 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION The present invention relates to a sectional boiler for burning of gaseous fuels by a flameless combustion process, in which the heat transmission by radiation is effectively utilized, a perfect combustion of the gaseous fuel at a very small excess of air is achieved and the combustion of the fuel proceeds in the most efficient part of the boiler at the surface of an articulated ceramic body under high temperatures.

According to Stefan-Boltzmanns Law a relatively considerable amount of heat is transmitted to the heating surface of the boiler as per the following equation:

C radiation coefficient T absolute temperature of the ceramic filling T temperature of the boiler wall A number of designs are known, in which the boilers operate on the principle of different flameless combustion methods. Boilers, in which gaseous fuel is burned by surface combustion in a layer of granulated refractory material, are capable of achieving high specific performances as well as high degrees of efficiency, but are unsuited for permanent operation, because their reaction speed is too high, upproportionately high temperatures are obtained and the granulated refractory material used, usually fireclay, is liable to meltdown and sinter after several days of operation, in consequence of which this type of boiler has to be put out of operation after a relatively short working period.

The composition of the gaseous fuel employed has considerable bearing on the reaction speed and, consequently, on the height of the combustion temperature. Hydrogen present in the gas, for example, leads to rapid and hardly controllable combustion reaction at the surface of the ceramic material used. The high temperatures are then the cause of an undesirable melting down of the ceramic material. Moreover, up to now no solution to the problem of an automatic control of the operation of these boilers has been found.

In boilers of another design the mixture of gas and air passes through, and burns in, a layer of granulated ceramic material and the combustion products transmit their heat by convection to a pipe-system of the boiler. Boilers of this type operate likewise with a high efficiency, have however large dimensions, because the radiation of the solid material is utilized to a small extent only, the major part of the heat being transmitted by convection.

Further known are boilers for flameless combustion in ceramic channels, in nozzles provided in refractory blocks or in porous refractory diaphragms. It is a common drawback of these as well as of the aforementioned boilers that in spite of a perfect combustion process and high efficiency, they have to be equipped with large convection surfaces and combustion spaces and this is the reason, why boilers of these types are bulky and heavy, their manufacture and operation uneconomical and require, moreover, manual servicing and, if possible, a permanent uninterrupted operation, because the starting of such boilers is unreliable and difficult.

SUMMARY OF THE INVENTION The present invention aims at eliminating the majority of the aforementioned disadvantages by providing a new sectional boiler for flameless combustion of gaseous fuels. The boiler is equipped with a jacket, a gas-air mixing device arranged in front of the boiler and with a water space or jacket constituted by at least two hollow sections, the cavities therein forming reaction chambers filled with a ceramic filling.

According to the main feature of the invention a porous refractory diaphragm accomodated in a distributor of the gas-air mixture in the inlet part of the boiler is connected to the supply of the gas-air mixture and behind said diaphragm a combustion space with a spark member for igniting the gas-air mixture is arranged and, behind the combustion space, a refractory block is accommodated, provided with apertures leading to said reaction chambers.

A furhter feature of the invention consists therein that the water space or jacket of the boiler is constituted by outer boiler sections or intermediate boiler sections, whose inner surface are of a comb-like formation.

In accordance with another feature of the invention the ratio of the distance between the opposite inner walls of the cavities in the various boiler sections, parallel to separating planes (or contact surfaces) between the sections, to the height of the reaction chambers amounts to 1:5 up to 1:8.

The sectional boiler according to the invention permits a continuous and safe operation, even with gases which are conventionally used in consumers gas distribution networks.

In the novel boiler three different processes of flameless combustion proceed simultaneously, namely in the combustion space at the outlet surface of the porous refractory diaphragm, in the refractory block and in the ceramic filling of the reaction chambers formed between the boiler sections. Due to this fact conditions are created for a reduction of the maximum combustion temperature and for the prevention of sintering or melting through of the ceramic filling in the reaction chambers between the boiler sections. Furthermore, due to the ratio of the distance between the opposite inner walls of the cavities in the boiler sections, parallel to the contact surfaces (separating planes) between the boiler sections to the height of the reaction chambers varying between 1:5 to 1:8, an effective burning or gaseous fuel of any kind and composition is made possible. The new design of the boiler is suited for automatic starting and control thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show diagrammatically an exemplary embodiment of the sectional boiler according to the invention.

FIG. 1 is a sectional view along the line B.B from FIG. 2 and shows the boiler in a longitudinal section.

FIG. 2 is a cross-sectional view along the line A--A from FIG. 1, and

FIG. 3 is a similar cross sectional view of a modified embodiment of the boiler.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing shows a vertical sectional boiler marked in general with the reference numeral C, made e.g., of cast iron, which will be disclosed in detail hereinafter.

Arranged in front of the boiler C is an air duct 1 and a gas duct 2 with a mixing device 3 to which a supply pipe 21 conducting the gas-air mixture to the boiler C is attached. Connected to said supply pipe 21 in the inlet part of the boiler C is a porous refractory diaphragm 5 made of ceramic material and accomodated in a distributor of the air-gas mixture. Arranged behind said diaphragm 5 is a combustion space 6 equipped with a spark member for igniting the gas-air mixture.

A refractory block 7, of ceramic material, is placed behind said combustion space 6 and provided with a number of apertures 8 leading to reaction chambers 10, which are constituted by the cavities formed in hollow outer boiler sections 17 and an intermediate boiler section 18, (FIG. 2) said boiler sections 17, 18 defining a water space or jacket 19 of the boiler. The reaction chambers 10 of an approximately hexagonal crosssection, are filled with a gas-permeable ceramic filling 9 having channels with a relatively large and rough surface. In FIG. I only the left hand reaction chamber 10 is shown as filled with the ceramic filling 9, the right hand chamber 10 is shown empty, i.e., before the filling 9 is inserted. The inner surfaces of the outer boiler sections 17 and of the intermediate boiler section 18 have a comb-like shape, the longitudinal axis of the individual combs extending in vertical direction.

The boiler as shown in the exemplary embodiment, is arranged for burning coke oven gas and, for this reason, a ratio of 1:6 is chosen between the distance D of cavities in opposite inner boiler section walls 15,16, parallel to the contact surfaces (separating planes) between the boiler sections 17,18, and the height E of the reaction chambers 10. The boiler sections 17, 18 are sealed by means of seals 13 inserted in suitable sealing grooves and are connected by shrunk-on collars pressed into hubs 14. Behind the reaction chambers 10 the boiler is closed by a collector ll of combustion products leading to a flue way 12.

A further one or more intermediate boiler sections 18 may be included into the system of boiler sections as shown in FIG. 3, so that the number of reaction chambers 10 is increased. All reaction chambers 10 have an equal nominal output, the total boiler output being a product of the nominal output of one reaction chamber 10 and the number of such chambers 10. In dependence on the possibilities of manufacture or requirements placed on the boiler operation, the crosssectional shape of reaction chambers 10 may be other than hexagonal. Crushed ceramic material of a predeterminal lump size can be used as ceramic filling 9.

Compressed air is fed through the air duct 1 into the mixing device 3, into which gas is sucked from the gas duct 2. The mixture of gas and air is supplied by the supply pipe 21 into the porous refractory diaphragm 5, accomodated in the distributor 4 and from here to the combustion space 6, where it is ignited by the spark member 20.

At the outlet surface of the porous refractory diaphragm 5 a primary flameless combustion of the gas is in progress, while in the combustion space the gas burns away partially. A small part of the heat from the combustion space 6 is transmitted to the water contained in the water space or jacket 19. The system of apertures 8 in the refractory block 7, situated in front of the inlet portions of the reaction chambers 10, serves to increase the combustion space 6. At the surface of the refractory block 7 a flameless surface combustion of the gas-air mixture is in progress. In the vicinity of the block 7 a further portion of the heat is transmitted to the water present in the water space or jacket 19. Though the refractory block 7 has a relatively samll surface area, the combustion at its surface occurs with such an intensity, that a high degree of heat transmission by radiation is achieved.

The relatively robust walls of the refractory block 7 prevent the deformation or sintering of the ceramic material, from which the refractory block 7 is made. The burning mixture of gas and air proceeds further to the ceramic filling 9 of the reaction chambers 10, where a highly intense flameless combustion at the surface of said filling 9 takes place. This applies in the event that the ceramic filling 6 consists of a gas permeable ceramic material or crushed ceramic material.

It will therefore be apparent, that the ceramic diaphragm 5 represents some sort of an end portion of a burner for flameless combustion, where the burning process begins. During operation the glowing diaphragm radiates thermal energy. This is substantially one type of flameless combustion.

In the art seven types of flameless combustion are usually distinguished (see for example the book by M.B. Ravid: Flameless surface combustion edition 1951, page 66). The boiler according to the invention operates with three types of flameless combustion simultaneously. It is the combustion on the diaphragm, in the refractory block and in the ceramic filling of the reaction chambers, as disclosed above.

A highly intense heat exchange by radiation occurs here in addition to a simultaneous heat exchange by conduction and convection. The heat exchange proceeds through the walls of the reaction chambers 10 into the water space or jacket 19 of the boiler. During their further advance towards the collector 11 the combustion products transmit their heat by convection to the water and to further layers of the ceramic filling 9, which simultaneously transmits the heat to the water by radiation with a lower intensity and by conduction. The combustion products are properly cooled down in the ceramic filling 9 and withdrawn from the various reaction chambers 10 through the collector 11 and flueway 12 into a chimney.

The ratio 1:5 to 1:8 between the distances D:E i.e., the distance between the opposite walls in the boiler sections and the height of the reaction chambers is most favorable as far as the economy of heat transmission to the walls and to the water jacket is concerned. If the ratio were smaller than 1:5, the combustion products leaving the boiler would have a high temperature, which would mean that the heat of the combustion products would not be sufficiently utilized. In the upper part of the reaction chambers, where the ceramic filling does not radiate any more, heat is transmitted by convection, which is less intense than the heat transmission in the part of the boiler containing the glowing ceramic filling, where the heat transmission proceeds by radiation.

If the ratio were higher than 1:8, the reaction chambers would be too high, so that the combustion products would be undercooled and moreover the increase in height of the chambers would lead to an increase in the weight of the boiler sections, out of proportion to the negligible amount of heat gained by such increased height of the chambers.

The sectional boiler embodying the invention can be used for central hot water heating, for heating of supply water over a heat exchanger and for similar purposes. In connection with a drum-shaped evaporator, placed above the boiler, it can be used also for steam heating. The generated steam or heating water should not be used for technological purposes and the boiler continuously filled with fresh water, because removal of the boiler incrustation is rather difficult.

We claim:

1. A sectional boiler for flameless combustion of gaseous fuels, comprising in combination:

a. at least two hollow boiler sections having cavities formed in at least one of their surface,

b. a water jacket constituted by said hollow boiler sections,

c. reaction chambers formed by said cavities in the juxtaposed boiler sections,

d. ceramic filling inserted in said reaction chambers,

e. an air duct, a gas duct and an air-gas mixing device for supplying gaseous fuel mixture to the boiler, arranged in front of the latter, f. a fuel supply pipe leading from the mixing device to the boiler, g. a fuel distributor connected to said fuel supply pipe and provided in the fuel inlet part of the boiler, h. a porous refractory diaphragm in said fuel distributor, i. a combustion space behind the refractory diaphragm, j. a spark member for igniting the gaseous fuel in the combustion space and k. a refractory block provided with apertures accomodated behind said combustion space and in front of said reaction chambers. 2. A sectional boiler as in claim 1, wherein the hollow boiler sections have opposed surfaces of a comb-like formation.

3. A sectional boiler as in claim 1, wherein the water i jacket of the boiler is constituted by hollow outer and tion chambers amount to 1:5 to 1:8. 

1. A sectional boiler for flameless combustion of gaseous fuels, comprising in combination: a. at least two hollow boiler sections having cavities formed in at least one of their surface, b. a water jacket constituted by said hollow boiler sections, c. reaction chambers formed by said cavities in the juxtaposed boiler sections, d. ceramic filling inserted in said reaction chambers, e. an air duct, a gas duct and an air-gas mixing device for supplying gaseous fuel mixture to the boiler, arranged in front of the latter, f. a fuel supply pipe leading from the mixing device to the boiler, g. a fuel distributor connected to said fuel supply pipe and provided in the fuel inlet part of the boiler, h. a porous refractory diaphragm in said fuel distributor, i. a combustion space behind the refractory diaphragm, j. a spark member for igniting the gaseous fuel in the combustion space and k. a refractory block provided with apertures accomodated behind said combustion space and in front of said reaction chambers.
 2. A sectional boiler as in claim 1, wherein the hollow boiler sections have opposed surfaces of a comb-like formation.
 3. A sectional boiler as in claim 1, wherein the water jacket of the boiler is constituted by hollow outer and intermediate boiler sections, at least some walls of said boiler sections being of a comb-like formation.
 4. A sectional boiler as in claim 1, wherein the ratio of the distance between the opposite inner walls of the cavities in the boiler sections, parallel to the contact surfaces of the boiler sections, to the height of the reaction chambers amount to 1:5 to 1:8. 